This invention relates to an electronic timepiece and in particular to an electronic timepiece having a monolithically integrated circuitry actuated by potentials of differing magnitude.
Because the power consumption of the electronic circuitry in an electronic timepiece has been significantly reduced by the use of complementary metal oxide semiconductor (C-MOS) transistors, their use has gained wide acceptance. Nevertheless, the power consumption of C-MOS transistors is relatively higher in the electronic timepiece circuit portions operating at high frequency signals such as the oscillating circuit and the high frequency divider stages of the frequency divider circuit, so that it is desirable that such circuits be actuated by potentials maintained at as low a level as possible. On the other hand, the driving circuit portion utilized to drive a time display requires considerably more power and is actuated at a higher potential than the higher frequency circuit portions. Moreover, as time display mechanisms have progressed from analogue systems utilizing hands and a dial disc, to digital systems utilizing light-emitting diodes or liquid crystals, a larger current and higher voltage has been required to drive same. Thus, the potential at which the different circuit portions in an electronic timepiece operate at optimal efficiency are different.
Heretofore, electronic watch circuitry has been monolithically integrated into a single circuit chip and a single power source utilized to actuate all the circuitry at one potential or separate chips are provided for the low and high potential circuit portions. When a digital display is comprised of liquid crystals, the driving circuit requires a relatively high voltage in the range of 3 to 6 volts. Nevertheless, such a range causes unnecessarily high breakdown voltages in the high frequency circuit elements such as the oscillator and dividing circuits, the consequence thereof being the necessity to increase the size of the chip and hence increase the power consumption thereof.
On the other hand, when light-emitting diodes are utilized, although such light-emitting diodes are capable of being actuated by low voltages in the range of 1.5 volts, such light-emitting diodes require relatively large currents. Thus, if a potential of 1.5 volts is utilized, it is impossible to drive the display because enough current is not available making it necessary to increase the size of the driving circuit for driving the light-emitting diode display.